Unlike men, who go by the "Mr." designation, it's not always easy to know how to address women, who might go by "Ms.," "Miss" or "Mrs." If you are unsure how to address a woman in a business letter, a good first step is to locate any business correspondence your female recipient has sent or signed so you can duplicate her preference. If you don't have or can't find any correspondence, use Ms. if you are unsure of her married status, Mrs. if you know she is married, and Miss if she is single. A strict exception is if she has a title such as Doctor.
When a woman has a professional title, use that title in lieu of Ms., Mrs., or Miss. For example, Ms. Ann Smith, a physician, becomes Dr. Ann Smith. If she has a Ph.D. it’s best to use her preference: either Ph.D. after her name or the Dr. title preceding it. If she is a reverend, her title is The Reverend. For attorneys, type “Attorney at Law” on the second address line, or use Esquire or Esq. after her name.
Use any professional designations after the woman's name, such as CPA for Certified Public Accountants, or MSW for Masters of Social Work.
When confronted with a gender-neutral name, such as Chris, use the first and last name. You can also use the job title, such as “Human Resources Manager, Chris Smith.” If a woman has two non-hyphenated last names, use both or the one you know she uses professionally.